1. Field of the Invention
This application relates generally to a method and apparatus for filtering an electric signal and, more specifically, to an electric heating appliance comprising an AC line filter without a grounding capacitor to limit earth leakage currents.
2. Description of Related Art
Electric appliances such as an electric range converts AC electric current introduced to the range into heat for elevating the temperature of food, for example. Like any electric device, electric appliances are made up of electronic and electric components that store and discharge a portion of this electric current. The electric current discharged from the components, commonly referred to as leakage current, is typically conducted to ground by a protective conductor including a grounding capacitor coupled between the AC line and ground. Without the protective conductor and grounding capacitor, the leakage current could potentially be discharged through any conductive part, or a surface of a non-conductive part of the electric range through any, possibly undesirable, conductive path to ground.
A power AC line filter can also be provided to an electric appliance to attenuate at least a portion of the electromagnetic interference (“EMI”) conducted along the AC power line of those appliances. The protective conductor and grounding capacitor combination that discharges the leakage current is included in such EMI filters to shunt high-frequency interference from the AC electric current to ground in addition to discharging the leakage current. The EMI filter has traditionally been provided to electric appliances at the AC input where the AC electric current is introduced to the electric appliance. In such a location, the EMI filter including the protective conductor and grounding capacitor can attenuate the EMI seen by the AC mains.
The design of conventional EMI filters including the grounding capacitor for discharging the leakage current has been limited by competing design interests. On the one hand, the value of the leakage current discharged via the grounding capacitor is a function of, and optionally proportional to, the capacitance value of the grounding capacitor. By minimizing the capacitance value of the grounding capacitor, the undesired leakage current can also be minimized.
But on the other hand, the degree of attenuation achievable by the EMI filter can also be a function of, and optionally proportional to, the capacitance value of the grounding capacitor. Increasing the capacitance value of the grounding capacitor increases the effectiveness of the EMI filter in attenuating radio-frequency and other noise having a high frequency relative to the frequency of the AC electric current. Thus, electric appliances provided with traditional EMI filters including the grounding capacitor have required balancing the desire to limit the leakage current through the grounding capacitor and the desire to attenuate the EMI in the AC electric current.